The present invention relates to an ink-jet printing method and ink-jet printer for printing an image on a printing medium by driving print elements of a printhead and ejecting ink in accordance with an image signal.
Conventionally, as printers for printing images on printing media (to be referred to as printing sheets hereinafter) by selectively driving print elements in accordance with print signals input from external devices such as host computers, printers based on the wire dot scheme, thermal transfer scheme, ink-jet schemes, and the like are known. Of these printers, an ink-jet printer, which incorporates an ink-jet printhead to print images by discharging ink from orifices (nozzles) of the printhead, can print high-resolution images, and is inexpensive. Owing to these advantages, this printer has recently attracted a great deal of attention, and is increasingly used in various fields. There is increasing demand for an ink-jet printer for color printing or gray-scale printing, in which a plurality of printheads, each having a plurality of ink channels and print elements with discharge energy generating elements arrayed at a fine pitch, are arranged in a direction (main scanning direction) perpendicular to the array direction (sub-scanning direction) of the plurality of print elements, and an image is printed by scanning these printheads in the main scanning direction.
In the above printhead, heating resistors serving as discharge energy generating elements are arranged at positions corresponding to the respective nozzles, and heat energy is generated by flowing a current in heating resistors. A liquid is then discharged from the corresponding nozzles by using the heat energy, thereby printing an image. Since today""s demands for high-density, high-speed printing are especially high, a plurality of lines are generally printed by one scanning operation of the printhead in the main scanning direction. Therefore, a printhead having many heating elements arranged at a high density is used.
When high-density, high-speed printing is performed, neighboring nozzles of the printhead are driven at very short time intervals. For this reason, ink discharged from a given nozzle tends to be influenced by a pressure wave produced by ink discharged from adjacent nozzles. Consequently, the amount, discharge speed, and the like of ink discharged from the respective nozzles become unstable, resulting in a deterioration in the quality of printed images.
In addition, if a printing sheet is checked by an electrostatic chuck method in conveying the printing sheet, ink droplets flying from the printhead are charged before they reach the printing sheet, as shown in FIG. 12. As a consequence, ink droplets flying nearby repel each other and their flying directions interfere with each other. As a result, the landing position of each ink droplet on the printing sheet deviates from the correct position. This will degrade the quality of an image printed on the printing sheet, thus posing a serious problem.
The present invention has been made in consideration of the above prior art, and has as its object to provide an ink-jet printing method and ink-jet printer which can print a high-quality image by eliminating the mutual influences of neighboring print elements, which is occurred in an apparatus for conveying a recording sheet by using an electrostatic chuck method.
It is another object of the present invention to provide an ink-jet printing method and ink-jet printer which can print a high-quality image by eliminating the influences of ink droplets discharged from neighboring print elements (nozzles).
It is still another object of the present invention to provide an ink-jet printing method and ink-jet printer which eliminate the influences of ink droplets discharged from neighboring print elements (nozzles) and increase the capacity of a power supply for driving a printhead.
It is still another object of the present invention to provide an ink-jet printing method and ink-jet printer in which the print elements of a printhead are formed into a plurality of groups, and the groups are time-divisionally driven, thereby eliminating, at the current driving timing, the influences of pressure waves generated by print elements which discharged ink at a driving timing preceding the current driving timing.
It is still another object of the present invention to provide an ink-jet printing method and ink-jet printer which can print a high-quality image by eliminating the influences of ink droplets discharged from neighboring print elements (nozzles) even when a printing medium is conveyed by the electrostatic chuck method.
In order to attain the above described objects, an ink-jet printer of the present invention prints an image on a printing medium by driving print elements of a printhead and ejecting ink in accordance with an image signal. The printer comprises: division means for dividing a timing of driving a plurality of print elements of the printhead in accordance with an image signal into a plurality of driving timings; selection means for selecting one of print element groups, of a plurality of print elements of the printhead, which are spaced apart from each other at predetermined intervals corresponding to the number of driving timings; driving means for energizing and driving the print element group selected by the selection means in accordance with the image signal at one of the plurality of driving timings; driving control means for causing the selection means to select a next print element group by shifting a position of the print element selected by the selection means by a predetermined amount, after driving is performed by said driving means, and causing the driving means to drive the print element group; and control means for causing the driving control means to repeatedly drive until a plurality of print elements of the printhead are selected by said selection means and driven at the plurality of driving timings.
An ink-jet recording apparatus of the present invention records an image on a recording medium by driving recording elements of a recording head and ejecting ink in accordance with an image signal. The apparatus comprises:
conveyance means for conveying the recording medium by an electrostatic chuck method; and selection means for selecting recording elements which are separately located from each other among a plurality of recording elements of the recording head, as a group, that are substantially simultaneously driven; wherein the selection means selects the recording elements which are separated, such that a deterioration in image quality due to a landing position offset by an electrostatic power from said conveyance means can be suppressed.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.